Updated

The Latest on the caravans of migrants making their way through Mexico (all times local):

10:10 a.m.

Mexican immigration authorities so far haven't tried to detain migrants in largest caravan of Central Americans now walking through the southern part of the country. But it's a different story with the second, smaller caravan of migrants about 200 miles behind them.

A federal official who was not authorized to be quoted by name says 153 migrants were detained Wednesday during highway inspections in the southernmost state of Chiapas.

While the precise size of that caravan is unclear, that could be equivalent to about 10 percent of those participating.

Mexico's immigration agency does normally operate highway inspection checkpoints in the area near the Guatemalan border. But Wednesday's detentions appear to mark a shift in enforcement strategy toward the caravans.

Officials haven't tried to detain the first, larger group, instead offering free trips home or legal status in Mexico. But agents appear to be focusing on picking off smaller groups.

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7:05 a.m.

Thousands of Central American migrants have again resumed their trek through southern Mexico after failing find buses to carry them.

The group estimated to number some 4,000 set off before dawn from the city of Juchitan. Organizers say they've shifted the planned route and now are heading for the town of Matias Romero en route to the Gulf coast city of Veracruz.

That city is a common transit route toward McAllen, Texas.

The group took a day off from walking on Wednesday, resting and caring for swollen feet.

A second, smaller group of 1,000 or so migrants is more than 200 miles behind the first caravan. A third band of about 500 from El Salvador has made it to Guatemala, and a fourth group of about 700 set out from the Salvadoran capital Wednesday.